1. Field of the Invention
This invention relates to circuit breakers provided with both ground fault and arc fault trip circuits, and more particularly, to a common test button for actuating selectively a ground fault test circuit and an arc fault test circuit.
2. Background Information
Circuit breakers provide overcurrent and short circuit protection for electric power systems. In the small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. Such a device includes a bimetal which is heated and bends in response to a persistent overcurrent condition thereby unlatching a spring powered operating mechanism which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature attracted by the sizable magnetic forces generated by a short circuit also unlatches, or trips, the operating mechanism.
In many applications, the miniature circuit breaker also provides ground fault protection. An electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This signal energizes a shunt trip solenoid which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device.
Recently, there has been considerable interest in also providing protection against arcing faults. Arcing faults are intermittent high impedance faults which can be caused for instance by worn insulation, loose connections, broken conductors, and the like. Because of their intermittent and high impedance nature, arcing faults do not generate currents of sufficient instantaneous magnitude or sufficient average current to trigger the thermal-magnetic trip device. Consequently, separate electrical circuits have been developed for responding to arcing faults.
Ground fault protection circuits and arc fault protection circuits typically include test circuits for affirming their continued operability. Currently, separate test switches, each with its own test button, are provided for performing the ground fault and arc fault tests. However, the molded cases of the miniature circuit breakers have been standardized for interchangeable use in load centers. There is limited space available in the standardized miniature circuit breakers for all of the additional circuitry required for ground fault and arc fault protection, let alone the test circuits.
There is a need therefore for a circuit breaker providing ground fault and arc fault protection which has means for testing both the ground fault and arcing fault circuits and yet can be contained in the standardized molded cases of the miniature circuit breakers designed for use with existing load centers.
This need and others are satisfied by the invention which is directed to a circuit breaker incorporating ground fault protection having a ground fault test circuit and arc fault protection having an arc fault test circuit in which a common actuator selectively actuates a ground fault test switch and an arc fault test switch. The common actuator is preferably a rocker button which rotates in one direction from a neutral position to actuate the ground fault test switch, and rotates in the opposite direction from the neutral position to actuate the arc fault test switch. The common rocker button is biased to the neutral position preferably by a leaf spring having a first leg which biases the rocker button from a first position in which the ground fault test switch is actuated toward the neutral position and a second leg which biases the rocker button toward the neutral position from a second position in which the arc fault test switch is actuated. In a preferred form, the common rocker button has a body with a transversely extending pivot and the leaf spring has a center section extending transversely to an axis of the body extending through the pivot with the two legs converging toward the pivot and having confronting terminal portions.
Where the ground fault and arc fault test switches have spring arms forming one contact, the common rocker button has a first actuating finger which engages the spring arm of the ground fault test switch and a second actuating finger which engages the spring arm of the arc fault test switch. Preferably the common rocker button applies a preload to both of these spring arms with the rocker switch in the neutral position.
More particularly, the invention is directed to a circuit breaker having a housing, separable contacts mounted in the housing, an operating mechanism for opening the separable contacts in response to a trip signal, trip means for generating a trip signal in response to predetermined current conditions and including ground fault trip means for generating a trip signal in response to a ground fault and arc fault trip means for generating a trip signal in response to an arc fault. The circuit breaker further includes test means including a ground fault test circuit having a ground fault test switch for testing the ground fault trip means and an arc fault test circuit having an arc fault test switch for testing the arc fault means. A common test actuator is moveable to a first position for actuating the ground fault test switch and to a second position for actuating the arc fault test switch.